1. Field of the Invention
The present invention relates to a rigid-printed wiring board having via holes, and a production method of the rigid-printed wiring board.
2. Description of the Related Art
Printed wiring boards called copper paste through hole PWB (rigid-printed wiring boards) utilize copper clad laminates for rigid-printed wiring boards with a paper phenol or a paper epoxy used as a base.
Some of these kinds of the rigid-printed wiring boards (hereinafter abbreviated as PWB) often used in electronic appliances have a via hole 1000 as shown in FIGS. 8 and 9. The via hole 1000 is provided by filling a copper paste 1003 on copper foils 1002 on the front and rear sides of a rigid-printed wiring board substrate 1001, and it is used only for the electric conduction between the copper foils 1002 on the front and rear sides of the substrate 1001. That is, a component lead, or the like, is not provided through the via hole 1000, and thus it is a kind of the through hole to be used only for the conduction between the wirings on the front and rear sides of the substrate 1001. The diameter of the hole is, about 0.3 to 0.8 mm.
However, such a rigid-printed wiring board involves the following problems.
In general, it is completed by a step of filling a prepared hole of the via hole 1000 with the liquid copper paste 1003, a drying step at about 60 to 100xc2x0 C., and a thermal curing step at 150 to 160xc2x0 C. In the case the base is a paper phenol substrate, the volatile component such as methanol, 1-butanol, 2-methyl-1-propanol, formaldehyde, toluene and salicylaldehyde contained in the substrate resin component, and moisture contained in the paper material are generated as an out gas. This gives rise to a failure in the copper paste 1003, such as the burst (bulge) part 1004 as shown in FIG. 8 and the void (bubble) part 1005 as shown in FIG. 9.
Particularly in the case when a via hole is disposed in the solid copper foil part, since the solid copper foil on the substrate surface serves as a barrier to the out gas, the out gas to be discharged tends to concentrate at a via hole cross-section so as to cause the burst void phenomenon frequently.
Moreover, in the case of a paper epoxy substrate, although the amount is smaller than that of the phenol substrate, the out gas of the volatile component and moisture is generated similarly in the drying and thermal curing steps.
Accordingly, an object of the present invention is to provide a rigid-printed wiring board capable of solving the above-mentioned problems as well as preventing the burst or void phenomenon of the copper paste, and a production method of the rigid-printed wiring board.
A first aspect of the present invention is a rigid-printed wiring board comprising copper clad laminates with a paper phenol or a paper epoxy used as a base, wherein a through hole is provided in the vicinity of a via hole for filling a copper paste.
According to the first aspect, since the through hole is provided in the vicinity of the via hole for filling the copper paste, the out gas can be discharged from the through hole so that generation of the burst phenomenon or the void phenomenon can be restrained drastically.
A second aspect of the present invention is the rigid-printed wiring board according to the first aspect, wherein one or a plurality of the through holes are provided and the through hole has a circular shape
A third aspect of the present invention is the rigid-printed wiring board according to the first aspect, wherein one or a plurality of the through holes are provided and the through hole has a linear shape.
A fourth aspect of the present invention is the rigid-printed wiring board according to the first aspect, wherein one or a plurality of the through holes are provided and the through hole has a curved shape.
A fifth aspect of the present invention is a rigid-printed wiring board comprising copper clad laminates with a paper phenol or a paper epoxy used as a base, wherein a copper foil land for a via hole for filling a copper paste and a copper foil part in the periphery thereof are formed separately such that the copper foil land for the via hole and the copper foil part in the periphery thereof are connected electrically so as for a copper foil non-formation part to be provided between the copper foil land for the via hole and the copper foil part in the periphery thereof.
According to the fifth aspect, since the copper foil land for the via hole and the land in the periphery thereof are connected electrically so as for the copper foil non-formation part to be provided between the copper foil land for the via hole and the land in the periphery thereof, the out gas can be released from the surface without the copper foil so that generation of the burst phenomenon or the void phenomenon of the copper paste can be cut back.
A sixth aspect of the present invention is the rigid-printed wiring board according to the fifth aspect, wherein the copper foil land for the via hole and the land in the periphery thereof are connected electrically by a fine line copper foil land.
A seventh aspect of the present invention is a production method of a rigid-printed wiring-board comprising copper clad laminates with a paper phenol or a paper epoxy used as a base, comprising the steps of providing a through hole in the vicinity of a via hole for filling a copper paste, filling the copper paste in the via hole, drying as well as thermally curing it.
According to the seventh aspect, in filling the copper paste in the via hole, drying as well as thermally curing it, the out gas can be discharged from the through hole to the outside so that generation of the burst phenomenon or the void phenomenon of the copper paste can be restrained drastically.
An eighth aspect of the present invention is a production method of a rigid-printed wiring board comprising copper clad laminates with a paper phenol or a paper epoxy used as a base, wherein a copper foil land for a via hole for filling a copper paste and a copper foil part in the periphery thereof are formed separately such that the copper foil land for the via hole and the copper foil part in the periphery thereof are connected electrically so as for a copper foil non-formation part to be provided between the copper foil land for the via hole and the copper foil part in the periphery thereof, comprising the steps of filling the copper paste in the via hole, drying as well as thermally curing it.
According to the eighth aspect, in filling the copper paste in the via hole, drying as well as thermally curing it, the out gas can be released from the copper foil non-formation part provided between the copper foil land for the via hole and the land in the periphery thereof, that is, from the surface without the copper foil so that generation of the burst phenomenon or the void phenomenon of the copper paste can be cut back.